aws-elastichace: support `engine` property for User and UserGroup class

[mazyu36]

Is your feature request related to a problem? Please describe.
At the moment, User and UserGroup classes don't support the engine property.
The blocker CFn bug has been resolved. aws-cloudformation/cloudformation-coverage-roadmap#2199

• The Memcached engine does not support RBAC (User and UserGroup classes)
• The Redis engine supports IAM, Password Users, and No Password Users. Redis user groups can contain both Valkey users and Redis users.
• The Valkey engine supports IAM and Password Users, but does not support No Password Users. Valkey user groups can contain both Valkey users and Redis users, but No Password users cannot be included.

Would you be willing to help with a PR?

• Yes, absolutely
• Yes, with some guidance
• Unfortunately no time :'-(

Describe the solution you'd like

Add engine property to User and UserGroup class.

Describe alternatives you've considered

Use escape hatches.

Additional context

N/A